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# stuck on a c4 integration question watch

1. a question from a revision book. its one of those "find the volume of the solid generated."

the equation is y= x + 2/x^3

to do it you do pi integration y^2.

but what would y^2 be? do you take the whole thing and square it, like

(x + 2/x^3)^2
2. yes, square it, then rewrite the 1/x's in terms of indices
3. thats c3 isnt it?

and yes
4. Yes of course thats what you do, y= x + 2/x^3 constitutes one value, it must be multiplied by itself when squared.
5. ok thanks a lot. i was squaring the two terms separately, i think thats why i was getting it wrong.
6. ok i squared it. i got the answer

x^2 + 4(x^-2) + 4(x^-6)

is that right?

7. (Original post by zeke53in)
a question from a revision book. its one of those "find the volume of the solid generated."

the equation is y= x + 2/x^3

to do it you do pi integration y^2.

but what would y^2 be? do you take the whole thing and square it, like

(x + 2/x^3)^2

Now partial fractions.
8. (Original post by zeke53in)
ok i squared it. i got the answer

x^2 + 4(x^-2) + 4(x^-6)

is that right?

Which book are you using?
9. it's an old P3 textbook.
10. (Original post by zeke53in)
ok thanks a lot. i was squaring the two terms separately, i think thats why i was getting it wrong.
That is just indicative of how A level maths is no longer mathematical, its just about learning a process and repeating it.

(x + 2/x^3)^2 means "x + 2/x^3" many "x + 2/x^3", which must equal
x(x + 2/x^3) + 2/x^3(x + 2/x^3)

Real maths is logic, I think too much of A level maths is jsut about applying rules, anyone could do that and no disrespect to the author of this post, but it should take someone one second to look at that question and think what really does this mean? There is only one answer. Instead they are left wondering about bodmas or that stupid quadratic rule its pathetic.
11. (Original post by 122025278)
That is just indicative of how A level maths is no longer mathematical, its just about learning a process and repeating it.

(x + 2/x^3)^2 means "x + 2/x^3" many "x + 2/x^3", which must equal
x(x + 2/x^3) + 2/x^3(x + 2/x^3)

Real maths is logic, I think too much of A level maths is jsut about applying rules, anyone could do that and no disrespect to the author of this post, but it should take someone one second to look at that question and think what really does this mean? There is only one answer. Instead they are left wondering about bodmas or that stupid quadratic rule its pathetic.
Firstly, what's your point? Secondly on an academic help thread you are meant to help the OP, not insult his intelligence. You may be relatively new on TSR, but you should still realise that there ARE people out there who arn't as academic as yourself.
12. Its not an insult to him its a general point. Think about differentiation or integration.
Decrease the index by one and multiply the coefficient by the previous index
Just by applying that rule you could get 4-5 marks in an A LEVEL exam, don't you think thats pathetic?
And I have helped him, I explained it to him which is more than anyone else did, all they did was tell him what to do "No you square it" he obviously needs to know why, which further proves to me the lack of mathematical skill of most candidates
13. (Original post by 122025278)
Its not an insult to him its a general point. Think about differentiation or integration.
Decrease the index by one and multiply the coefficient by the previous index
Just by applying that rule you could get 4-5 marks in an A LEVEL exam, don't you think thats pathetic?
And I have helped him, I explained it to him which is more than anyone else did, all they did was tell him what to do "No you square it" he obviously needs to know why, which further proves to me the lack of mathematical skill of most candidates
That's true for C1 - 2 but if you attempt C3 - 4 or FP1 - 3 you will quickly realise that if that's all you know about differentiation and integration, you're pretty damn screwed...
14. I agree with '122025278', its pathetic to see a student who's upto the C4 module not knowing how to square a binomial.
15. So you're taking the apparent ability of one candidate, and extrapolating that to 'most' candidates?

Sounds dodgy to me.
16. i dont think it's "pathetic". if you see in the original post, i was just making sure that this is the way to do it. sometimes i get confused is all. i didnt ask for step by step. thanks to all the people who did help though.
17. (Original post by IChem)
That's true for C1 - 2 but if you attempt C3 - 4 or FP1 - 3 you will quickly realise that if that's all you know about differentiation and integration, you're pretty damn screwed...
Actually no, you prove to me how integration by substitution holds then? All your doing is using a formula
18. You want us to integrate and differentiate from first principals? everyone learns that when they start calculus (I assume) but it would be stupid to put it on the syllabus as people would just learn the process without knowing what is actually happening.
19. (Original post by 122025278)
Its not an insult to him its a general point. Think about differentiation or integration.
Decrease the index by one and multiply the coefficient by the previous index
Just by applying that rule you could get 4-5 marks in an A LEVEL exam, don't you think thats pathetic?
And I have helped him, I explained it to him which is more than anyone else did, all they did was tell him what to do "No you square it" he obviously needs to know why, which further proves to me the lack of mathematical skill of most candidates
Based on that logic, don't you think it's pathetic that splitting something into partial fractions can get you 5-7 marks?

The process itself is actually quite simple, and I'm sure a 14 year old could work it out with some thought and guiding in the right direction. If you don't like their rules, don't play the game, but you won't get the qualification.
20. (Original post by 122025278)
Actually no, you prove to me how integration by substitution holds then? All your doing is using a formula
Better to be making intelligent use of a formula that to be blindly regurgitating a proof.

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